Synchronized circuit interrupter with shunting impedance contacts



June 1966 F. KESSELRING ETAL 3,257,531

SYNGHRONIZED CIRCUIT INTERRUPTER WITH SHUNTING IMPEDANCE CONTACTS Filed Aug. 29, 1961 2 Sheets-Sheet 1 32 'Q- I l NON-SYNCHRONOUS I 27 OPER. MECHANISM 25 11 6 Fig. 3

MAGNETIC MATERIAL Flg. 4

INVENTORS Fritz Kesselring 8 Ernst Gisiger ATTORNEY June'zl, 1966 F. KESSELRING ETAL IMPEDANCE CONTACTS Filed Aug. 29, 1961 LOW PRESSURE HIGH 1 PRESSURE NON-SYNCHRONOUS 86 OPERATING MECHANISM SYNCHRONIZED CIRCUIT INTERRUPTER WITH SHUNTING z Sheets-Sheet 2 United States Patent 0 3,257,531 SYNCHRONIZED CIRCUIT INTERRUPTER WITH SHUNTING IMPEDANCE CONTACTS Fritz Kesselring, Kusnacht, Zurich, and Ernst Gisiger, Zurich, Switzerland, assignors to Siemens-Schuclrertwerke Aktiengesellschaft, Eriangen, Germany, a corporation of Germany Filed Aug. 29, 1961, Ser. No. 134,655 Claims priority, application Germany, Aug. 31, 1960, S 70,157 10 Claims. (Cl. 200-143) This invention relates to synchronized circuit interrupters in general and, more particularly, to improved synchronized circuit interrupters involving improved contact-operating arrangements.

In United States patent application filed March 22, 1961, Serial No. 97,656 entitled Synchronous Circuit Interrupting Devices, by Fritz Kesselring and Lutz Seguin, and assigned to the assignee of the instant application, there is proposed the use of a synchronous operator in connection with circuit interrupters to actuate contact movement and to control component parts of the circuitinterrupting structure.

It is a general object of the present invention to improve upon the synchronized circuit-interrupting structures of the aforesaid application rendering them of simplified nature and more applicable to modern circuit-interrupting structures.

Another object of the present invention is to provide an improved synchronized circuit-interrupting structure in which a pair of synchronous operators are employed, one of the synchronous operators being applicable to a moderate overload current level, whereas the other synchronous operator is applicable to a high-fault-current condition, the arrangement being selectively operable.

Still a further object of the present invention is to provide an improved synchronized circuit-interrupting structure of simplified construction and readily adaptable for low-voltage application.

A further object of the present invention is the provision of an improved fluid-blast circuitdnterrupting structure involving a pair of main contact structures and a shunting impedance means having series auxiliary contacts to reduce the rate of rise of the recovery voltage across the main contact structure to enable the circuitinterruptnig structure to interrupt higher power circuits.

Further objects and advantages will readily become apparent upon reading the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 illustrates a longitudinal sectional view taken through a synchronized circuit-interrupting structure embodying principles of the present invention, the contact structure being illustrated in the closed-circuit position;

FIG. 2 is a sectional view taken substantially along the line II-II of FIG. 1;

'FIG. 3 is a vertical cross-sectional view taken through a modified-type synchronous circuit-interrupting structure, the contact structure being illustrated in the closed-circuit position;

FIG. 3A is a detailed view of the manual operator for the synchronous interrupting device of FIG. 3;

FIG. 4 is a sectional plan view of the synchronized circuit-interrupting structure of FIG. 3;

3,257,531 Patented June 21, 1966 FIG. 5 is a vertical sectional view taken through a fluid-blast type of synchronized circuit-interrupting structure, the contact structures being illustrated in the closedcircuit position; and,

FIG. 6 is a sectional view through the circuit-interrupting structure of FIG. 5 substantially along the line VI VI thereof.

The present invention is particularly concerned with the use in synchronized circuit-interrupting structures of systems employing moving coils energized by the alternating current, which may serve as the tripping means, or opening means for such interrupting devices. The moving coils may actuate, for example, latches, valves, compressed gas rotary slide valves, or similar type structures. For this purpose, it is suflicient if the moving coil produces a torque of, for example, 0.1 cmkp. (centimeter-kilopond). Theoretical and experimental investigations lead to a surprising result, namely that the torque alternating current moving coil system increases with the fifth power of the linear dimension-s of the system. Correspondingly, increasing the linear dimensions to twice the original value results in an increase of the torque by a factor of substantially 30 times. In particular, for example, a torque of approximately 200 cmkp. can be produced by feeding a short-circuit current of approximately 10,000 amperes into a rectangular copper coil having dimensions of 3 centimeters by 7 centimeters. These large torques make it possible to build synchronous circuit-interrupting structures of particularly simple design. Such synchronous circuit-interrupting structures are characterized in that an inductance system, energized from the breaker current and consisting of at least one movable element, such as a rotating coil element, may be employed as the driving mechanism for the movable circuit breaker parts.

In most cases, it will be desirable to arrange the contact separation so that it takes places only when the circuit current is decreasing on the descending portion of the alternating-current wave, whether the circuit current is symmetrical, or asymmetrical, or whether it is a reverse current in a direct-current installation.

Referring to FIGS. 1 and 2 of the drawings, the reference numeral 1 generally designates a synchronous-type circuit-interrupting structure. The circuit interrupter 1 includes a pair of line terminal studs 2, 3 having relatively stationary contacts 4, 5 at their inner, or confronting ends. The reference numerals 6, 7 generally designate laminated iron, or magnetic systems which surround the line terminal studs 2, 3 respectively. The iron cores 6, 7 are provided with cylindrical bores 8, 9, concentrically of which are arranged the cores 10, 11. In the air gaps, which are formed in this manner, the rectangular coils 12, 13 revolve on their shafts 14, 15 on suitable journal supports, such as ball bearing supports 16, 17, 18 and 19, for example.

On the shaft extensions 14, 15 there are mounted movable bridging contacts 20, 21. These movable bridg-- ing contacts 20, 21 are pushed away from or toward the relatively stationary contacts 4, 5 by the movable coils 13, 12 respectively. The housing structure 22 for the circuit interrupter 1 may be comprised of a pair of cylindrical halves 23, 24 having flange portions 25, 26 which abut a suitable gasket member 27, as shown in FIG. 1. The interior of the housing structure 22 is filled with a suitable arcextinguishing medium, for example oil, or sulfur-hexafluoride (SP gas.

The magnetic cores 10, 11 form an air gap which is larger in the case of the magnetic system 6 than in the case ofthe magnetic system 7. In addition, the magnetic system 6 is provided with more turns on the coil 12. Biasing means 28, assuming the form of a toroidal spring coil, holds the movable bridging contact 21 normally in an open-circuit position, whereas biasing means 29, assuming the form of a toroidal spring coil, biases the bridging contact 2t), under normal operating conditions, against the stationary contacts 4, 5. By means of a suitable latch 30, the movable bridging contact 20 may be held in the open-circuit position against the force of the spring 29.

The synchronized circuit-interrupting structure 1, illustrated in FIGS. 1 and 2, functions in the following manner: In case of moderate overcurrents, the diminishing or decreasing main current induces in the moving coil 13 a secondary current which moves the movable bridging contact 20 into the open-circuit position. Upon the instant that the diminishing circuit current passes through its zero value, the arc is extinguished, and the movable bridging contact 20 is held in the open-circuit position by the latch 30. In case the arc is not interrupted for some reason, then the induction in the air gap of the magnetic system 7 changes its direction as explained in the aforesaid patent application, and a force in the opposite direction is developed in the moving coil 13 by which the movable bridging contact 20 is instantly moved again into the closed-circuit position, as shown in FIG. 2. When the instantaneous value of the circuit current decreases the next time, a synchronized interruption follows once more in the above described manner.

When a short-circuit current occurs, then there is developed in the moving coil 12 of the magnetic system 6 a very strong force in the closing direction. The movable bridging contact 21 is forced against the relatively stationary contacts 4, with considerable force. Simultaneously, the movable bridging contact 20 is moved away from the contacts 4, 5 into an open position by an impact member, or plunger pin 31 secured to bridging contact 21; and the movable bridging contact 20 is, consequently, latched in the open-circuit position by the latch element 30. Because the magnetic system 7 is saturated at high primary currents, no current is induced in the moving coil 13. In case of decreasing shortcircuit currents, the moving coil 12 rotates in the opposite direction, which opens the current circuit and interrupts the arc. The movable bridging contact 21 then remains under the effect of the spring 28 in the open position. If the arc interruption does not take place,

then the closing and opening process is repeated. Aftercompleting the are interruption process, the circuit breaker 1 is opened. In order to reclose it again, the latch 30, which may be a frictional latch, may be released by actuation of an operating mechanism 32 which is of the nonsynchronous type. After this occurs, the movable bridging contact 20 resumes its closed position, as shown in FIG. 2, under the effect of the biasing spring 29. For interrupting smaller values of currents, an additional device may be provided to assistin rotating the shaft 15 in the direction for opening. As shown in FIG. 1, this may include a shaft extension 33 extending exteriorly of the housing structure 22 by a suitably provided sealed opening.

The application of two magnetic systems 6, 7 with different air gaps and/or different numbers of turns on the coil elements 12, 13 has the advantage that also load-switching operation with synchronization can be made. On the other hand, however, the short-circuit bridging contact 21 takes over synchronous interrupting at high overloads and at short-circuit currents. The circuit interrupting structure 1 is simple and can be easily applied into existing line systems.

With reference to the modified-type synchronous circuit-interrupting structure 37 of FIGS. 3 and 4, it will be noted that there is provided a magnetic system 38 having an air gap 39. Movable in a linear direction within the air gap 39 is a rectangular coil element 40, which is connected through a holder 41 with a movable bridging contact 42. Beneath the coil 40 there is provided a pair of flexible spring-like extensions 43, 44,'whose lower latching ends engage with recesses 45, 46 in the open position. The reference numeral 47 designates the primary, or exciting winding carrying the main current. The horn-like stationary contacts 48, 49 are mounted on insulating plates 50, 51. The reference numeral 52 indicates a divergent arc-chute arrangement which may be of a rather conventional type.

Hand operation of the device 37 take-s place by means of a U-shaped holder 53, FIG. 3A, which is interconnected with an insulating bridging bar 54 by means of springs 55. The reference numeral 56 indicates an addit-ional spring which biases the movable contact 42 upwardly against the spaced relatively stationary contacts 48, 49 as shown in FIG. 3.

The main current terminal studs 57, 58 are mounted upon an insulating base plate 59. The primary, or exciting winding 47, is located between the main terminal stud 57 and the relatively stationary contact 48, whereas the relatively stationary contact 49 is connected directly to the main terminal stud 58, as shown. A suitable housing structure 60 is provided, preferably being made of insulating material.

The synchronized circuit-interrupting arrangement 37, illustrated in FIGS. 3 and 4, functions in the following manner: The hand-tripping or opening operation is obtained by pressing downwardly upon the holder 53, by which the springs 55 are compressed sufficiently until they overcome the force produced by the lower single spring 56. The circuit breaker 37 is then held in the open-circuit position by the latch elements 43, 44. The hand closing operation is analogously obtained by pulling upwardly upon the holder 53, whereby first the resistance of the latches 43, 44 is overcome, and then the movable contact system moves quickly upwardly particularly under the effect of the lower biasing spring 56. The movable elements will then move into the closed position illustrated in FIG. 3 of the drawings.

When an overcurrent occurs in the connected circuit, then a secondary current is induced in the rectangular coil element 40 which, together with the induction occurring within the air gap 39 results in a force on the closed-turn coil element 40 which has a downward direction and occurs when the line current is decreasing on the descending portion of the current wave. The circuit interrupter 37 will then move into the open-circuit position and is firmly held in this position by the latch elements 43, 44

as soon as the interruption has taken place at the next passage of the current through the zero valve. Otherwise, the eifect of the force on holder 41 is reversed, and the breaker 37 instantaneously recloses and opens again shortly before the next time that the circuit current passes through its zero value. Arc quenching action takes place in a known manner within the divergent arc chute structure 52, which may comprise one or more splitter members 52a, as shown in FIG. 3. As a result of the flexible coupling 61, comprising the springs 55, 56 the synchronous operation is not prevented by a simultaneous hand operation. The advantage of the circuit-interrupting arrangement set forth in FIGS. 3 and 4 is in its simple construction and the small amount of energy needed for its operation resulting from the synchronized control of the movable bridging contact 42. In many cases it is satisfactory to use, instead, of a divergent-type quenching system 52, only a bridging-type contact with a relatively small stroke, for example, approximately 0.6 millimeter. In such case, arc-quenching action may take place simply by axial cooling of the resultant arc. In this case, it may also be of advantage to use contacts made of an arc-resistant material, such as a silver cadmium alloy.

The reference numeral 72 designates the upper main line stud, which is mounted within an insulating cover 73.

The reference numeral 74 designates a movable contact which is provided on its sides with slots, in which the curved levers 75, 76 are engaged. A magnetic system 77 is provided within which are arranged coils 78, 79. The line terminal stud 86 constitutes a magnetomotive force means to generate magnetic flux in the magnetic circuit. The coils 78, 79 are connected with the rotating arms 80, 81 through their shafts 82, 83. The shaft 83 has attached to its lower end another lever 84. The movable contact 74 is electrically connected with the flexible spring segments 85 which are electrically connected directly to the lower main terminal stud 86 mounted within an insulating cover 87.

A second auxiliary movable impedance contact 88 is provided, which is electrically connected on the one end to the main contact stud 86, and on the other hand to a nozzle-like relatively stationary contact 89. The movable auxiliary impedance contact 88 may pass with sliding contact through a bore provided in the lower main terminal stud 86 itself. At the left-hand end of the movable auxiliary contact 88 there is provided a connection to an insulating operating rod 90. As a result, the movable impedance contact 88 can be moved back and forth either by the lever 84 or by the insulating operating rod 90.

The breaker is enclosed within a housing 91, which is mounted upon insulators 92, 93. The interior of the insulator 92 is connected with a low pressure container 94, whereas the supporting insulator 93 opens into a highpressure reservoir tank 95. The reference numeral 96 designates a suitable operating mechanism compartment, which is attached, by means not shown, to a supporting wall structure 97. The shaft 83 of the moving coil element 78 has attached at its upper end an insulating valve baffle member 98, which is moved against a sealing ring 99 when the breaker is in the open-circuit position.

To assist in lowering the rate of rise of the recovery voltage and thereby to enable the breaker to interrupt high-power circuits, there is preferably provided a shunting impedance means 100, assuming the form of a resistor, which is connected on the one end to the relatively stationary contact 89 through a metallic tube 101 and on the other side with a metallic cap 102 which, in turn, is electrically connected to the main terminal stud 72 through a terminal screw 103 and the metallic terminal plate 70. The reference numeral 104 designates the insulating resistor housing. An auxiliary contact valve piston 105 is provided with small openings 106 on its lefthand side, as viewed in FIG. 5. It has attached thereto an arcing pin 107, whereas a compression spring 108 acts against the right-hand side thereof. The reference numerals 109, 110 designates suitable sealing rings, the function for which is more clearly understandable from the description hereinafter provided.

The synchronized circuit interrupting structure 66, as set forth in FIGS. 5 and 6 of the drawings, functions in the following manner: When the insulating operating rod 90 moves toward the left, by means of the expansion-compression spring 111, constituting a flexible coupling means 112, then the shaft 83 and with it also the lever 80 are moved by the lever 84 in such manner that the curved lever 76 moves in a clockwise direction. In thismanner, the movable contact 74 is pushed downwardly and compressed fluid, such as compressed air, flows through the nozzle 67 and the resultant arc is extinguished when the current passes through its value. The closing operation is achieved by moving the insulating rod toward the right in a corresponding manner. Such motion of the insulating operating rod 90 may be achieved by an externally situated operating lever 113 connected to a nonsynchronous operating rod 114, as indicated in FIG. 5 of the drawings.

In general, it is of advantage to provide a certain amount of lost motion between the levers 76 and 75 and the movable contact 74, so that the latched position, which is provided by rollers 115 is overcome in an impact-like manner.

When an overcurrent occurs, then the levers 80 and 81 are rotated with a rather large force by the coils 78 and 79 toward an open position when the instantaneous value of the circuit current is decreasing, and toward a closed position when the circuit current is increasing in its instantaneous value. Simultaneously also, the contact 88 is moved by the lever 84 toward the left when the circuit current is decreasing. .The impedance means, or resistance is connected in parallel with the main interrupting gap, and this makes the interruption of the main current much easier because of the depressing effect which is exerted upon the rate of rise of the recovery voltage. Following the interruption at the main contacts, there also occurs interruption between the auxiliary contacts 88, 89. There will be a following travel of the piston arcing contact to the left, as viewed in FIG. 5, as auxiliary contact 88 moves to the left, so that the residual current are drawn between contacts 88, 105 may be ex tinguished, say one-half cycle later than the extinction of the main current are drawn between main contacts 67, 74.

From the foregoing, it will be apparent that there first occurs interruption between the main contacts 67 and 74 and then subsequently the auxiliary impedance contacts 88 and 89 are separated, as pointed out above. The compressed fluid, such as compressed air, flows under high pressure through the resistor housing 104 and through the upper narrow opening 116 to the low-pressure tank 94. This results in fast interruption of the residual current are carried by the resistance 100 when this current passes through its zero value. Subsequent to the foregoing interruption, the insulating valve bafi le 98 takes a position in front of the opening in the relatively stationary contact 67 and is firmly held in this position against the seal 99 by the differential gas pressure.

As soon as the movable auxiliary contact 88 moves away from the seal 109, the valve piston 105 is driven by the high pressure compressed gas toward the right, by which an arc is drawn between the point of contact pin 88 and the arcing pin 107 which carries the residual current as reduced by theresistance 100. This arc will be quenched when the current passes through its zero value. In the meantime, the pressure within the housing 104 is increasing, whereby the openings 106 in the valve piston 105 have a larger area than the relatively restricted opening 116. The result of this is that the valve piston 105 is driven by the spring 108 toward the left, as viewed in FIG. 5, as a result of an equalization of the gas pressure on both of its sides. As a result, the arcing pin 107 is moved against the sealing ring 110, which further seals off the breaker housing 91 at this point. The pres sure against the spring 108 is now given by the crosssectional area of the arcing pin 107 at its exposed area to the sealing ring 110. This pressure is, of course, less than the force exerted by the spring 108 so that a satisfactory seal is obtained. If for any reason, the arc quenching action does not take place at this first controlled passage of the current through its zero value, then the circuit breaker will reclose and synchronized opening will take place, as described, at the next passage of the current through its zero value. If the circuit interrupter is used as a reversing switch, then it will be of advantage an induction-type system. Because of the low arcing energy, the interrupting contacts can be built at the same time as valve elements and, therefore, several other valves can be eliminated. In addition, the interrupting capability of the circuit interrupter 65 is considerably improved by the additional provision of a parallel resistance 100.

From the foregoing description of several types of synchronous circuit-interrupting structures, it will be apparent that improved operation with light-weight elements may readily be achieved, and a relatively small amount of arc-extinguishing fluid may be employed.

Although there have been illustrated and described specific structures, it is to be clearly understood that the same were merely for the purpose of illustration, and that changes and modifications may readily be made therein by those skilled in the art Without departing from the spirit and scope of the invention.

We claim as our invention:

1. A synchronous-type alternating current fluid-blast circuit interrupter including separable main contacts, impedance means shunting said separable main contacts, a pair of separable auxiliary contacts disposed in series relationship with said impedance means, operating means for eflectin'g separation of said separable main contacts including a synchronous operator, said synchronous operator including a magnetic circuit having an air gap, magnetomotiveforce means responsive to the alternating current to be interrupted for generating magnetic flux in said magnetic circuit dependent upon the current to be interrupted, a moving coil element disposed within said air gap, means for producing a current in said moving coil element dependent upon the rate of change of the current to be interrupted, said operating means functioning to separate said main contacts to draw a main current arc, and means interrelating actuation of said synchronous operator with opening motion of the separable auxiliary contacts to'draw a residual current-arc.

2. The combination in a synchronous-type alternatingcurrent fluid-blast circuit interrupter of means defining a course of fluid under pressure, a relatively stationary orifice-type main contact, a cooperable movable main interrupted, impedance means including series auxiliary contacts shunting the main contacts, and means correlating opening movement of the moving coil element'with opening movement of one of the auxiliary contacts to draw a residual-current arc.

3. The combination according to claim 2, wherein a non-synchronous operator is provided for opening the movable main and auxiliary contacts, and flexible coupling means interconnects the induction-type synchronous operator with the non-synchronous operator so that synchronousoperation may override non-synchronous operation.

4. The combination as set forth in claim 2, wherein the movable main contact serves as a blast valve for controlling a blast of fluid through the orifice-type main contact, and said moving coil element rotates a closure baffle plate over the orifice opening to halt the fiuid blast during the end of the opening operation.

5. The combination according to claim 2, wherein means are provided to force a fluid-blast adjacent the auxiliary contacts to facilitate extinction of the residualcurrent arc.

6, The combination according to claim 5, wherein valve-piston means are provided for halting the fluidblast adjacent the auxiliary contacts toward the end of the opening operation.

7. A synchronous-type alternating-current fluid-blast circuit interrupter of the type using a closed gas system including a relatively stationary main orifice-type contact, a cooperable valve-type movable main contact, a housing, a bypassing impedance housing enclosing impedance means shunting said main contacts, a pair of auxiliary impedance contacts in series relationship with the impedance means, operating means for opening said main valveatype movable contact including a synchronous operator, said synchronous operator including a magnetic circuit having an air gap, magnetomotive force means responsive to the alternating current to be interrupted for generating magnetic flux in said magnetic circuit dependent upon the current to be interrupted, the moving coil element disposed within said air gap, means for producing a current in said moving coil element dependent upon the rate of change of the current to be interrupted, connecting means interrelating actuation of said synchronous operator with opening .motion of the auxilsecond supporting insulator for said housing, and a gas compressor is provided for compressing gas from the lowpressure region and forcing it into the high-pressure region.

9. A synchronous-type alternating-current fluid-blast circuit interrupter of the type using a closed gas system including a relatively stationary main orifice-type contact, a cooperable valve-type movable main contact, a housing, a bypassing impedance housing enclosing impedance means shunting said main contacts, a pair of auxiliary impedance contacts in series relationship with the impedance means, operating means for the valve-type movable main contact including a synchronous operator, said synchronous operating including a magnetic circuit having an air gap, magnetomotive force means responsive to the alternating current to be interrupted for generating magnetic flux in said magnetic circuit dependent upon the current to be interrupted, a moving coil element disposed within said air gap, means for producing a current in said moving coil element dependent upon the rate of change of the current to be interrupted, connecting means interconnecting actuation of said synchronous operator with opening motion of the auxiliary impedance contacts, non-synchronous opening means having a flexible connection with said synchronous operator, and a valve bafile plate carried by said moving coil element to close the opening through the orificetype main contact and thereby halt the gas blast therethrough toward the end of the opening operation.

10. The combination in a synchronous-type alternating-current fluid-blast circuit interrupter of means defining a source of fluid under pressure, a relatively stationary orifice-type main contact, a cooperable movable main contact operating means for said movable main contact including a synchronous operator said synchronous operator including a magnetic circuit having an air gap magnetornotive force means responsive to the alternating current to be interrupted for generating magnetic flux in said magnetic circuit dependent upon the current to be interrupted a moving coil element disposed within said air gap means for producing a current in 9 19 said moving coil element dependent upon the rate of 2,672,541 3/ 1954 Paul 200148 change of the current to be interrupted lever means for 2,846,623 8/1958 Wolff 200111 interrelating movement of said moving coil element with 3,052,783 9/ 1962 Buron 200144 opening of the movable main contact non-synchronous FOREIGN PATENTS opening means and resilient coupling means interposed 5 between said synchronous operator and said non-syn- 718,985 11/1954 G e Brl-talnh a C meme means KATHLEEN H. CLAFFY, Primary Examiner.

References Cited by the Examiner BERNARD GILHEANY Examiner UNITED STATES PATENTS 10 ROBERT s. MACON, Assistant Examiner. 2,108,560 2/1938 Kesselring 200148 2,222,719 11/1940 Prince 200144 

2. THE COMBINATION IN A SYNCHRONOUS-TYPE ALTERNATINGCURRENT FLUID-BLAST CIRCUIT INTERRUPTER OF MEANS DEFINING A COURSE OF FLUID UNDER PRESSURE, A RELATIVELY STATIONARY ORIFICE-TYPE MAIN CONTACT, A COOPERABLE MOVABLE MAIN CONTACT, OPERAING MEANS INCLUDING AN INDUCTION-TYPE SYNCHRONOUS OPERATOR FOR EFFECTING OPENING MOVEMENT OF SAID MOVABLE MAIN CONTACT, SAID SYNCHRONOUS OPERATOR INCLUDING A MAGNETIC CIRCUIT HAVING AN AIR GAP, MAGNETOMOTIVE FORCE MEANS RESPONSIVE TO THE ALTERNATING CURRENT TO BE INTERRUPTED FOR GENERATING MAGNETIC FLUX IN SAID MAGNETIC CIRCUIT DEPENDENT UPON THE CURRENT TO BE INTERRUPTED, A MOVING COIL ELEMENT DISPOSED WITHIN SAID AIR GAP, MEANS FOR PRODUCING A CURRENT IN SAID MOVING COIL ELEMENT DEPENDENT UPON THE RATE OF CHANGE OF THE CURRENT TO BE INTERRUPTED, IMPEDANCE MEANS INCLUDING SERIES AUXILIARY CONTACTS SHUNTING THE MAIN CONTACTS, AND MEANS CORRELATING OPENING MOVEMENT OF THE MOVING COIL ELEMENT WITH OPENING MOVEMENT OF ONE OF THE AUXILIARY CONTACTS TO DRAW A RESIDUAL-CURRENT ARC. 